Olympic 100m champion Justin Gatlin has appealed to the Court of Arbitration for Sport (Cas) against his four-year ban for failing a drugs test in 2006.

The 25-year-old was initially banned for eight years by the United States Anti-Doping Agency (Usada) but it was reduced after an appeal this week.

But Gatlin could now be cleared in time to compete at the Beijing Olympics.

"Mr Gatlin is taking the next steps in recovering his right to defend his gold medal," said lawyer Maurice Suh.

"While there are many possible avenues that we are currently exploring, the appeal of the arbitration panel decisions are a critical component of his defence."

The athlete's other options include appealing to the International Association of Athletics Federations (IAAF) or filing a federal lawsuit.

Usada confirmed an arbitration panel had voted 2-1 for a four-year ban, meaning Gatlin will not be able to race until 24 May, 2010.

They've taken away everything I've worked hard for

Justin Gatlin

But if the appeal is successful it could clear the way for Gatlin to receive a two-year ban for the 2006 test and become eligible to compete in May, a month ahead of the US Olympic trials for the Beijing Games.

Gatlin, the 2005 world 100m and 200m champion, gave a positive test for testosterone at the low-level Kansas Relays in April 2006.

The American has accepted testing positive but claims he never knowingly used banned substances.

It was his second failed drugs test and, under the World Anti-Doping Agency (Wada) code, he should have been given a lifetime suspension.

But Usada, in exchange for Gatlin agreeing to cooperate with its anti-doping campaign and in recognition of the exceptional circumstances of his first failure, imposed an eight-year ban.

He failed his first test in 2001 when amphetamines were found in his samples at the USA Junior Championships.

But it was accepted that medicine he had been taking for 10 years to control attention-deficit disorder was the reason for the failed test.

Gatlin could press his case to the IAAF that an earlier doping violation in his career should not be counted against him and his ban should be reduced.

If the panel treated the 2006 violation as a first offence and cut the ban to two years, he could be reinstated in May, giving him time to qualify for the US Olympic Athletics Trials from 27 June.

"I know in my heart I haven't done anything wrong. I have been robbed. I have been cheated of an opportunity to finish my career," Gatlin told the Washington Post earlier this month.

"They've taken away everything I've worked hard for.

"I'm a fighter and I've been a fighter from the very beginning and I'm going to continue to fight.

"I feel like I got stuck in a bank that was being robbed and then they accused me of robbing the bank."